The present invention, in some embodiments thereof, relates to isolated polypeptides and polynucleotides encoding same for the diagnosis and treatment of VEGF-associated medical conditions.
Vascular endothelial growth factor (VEGF), an endothelial specific mitogen, plays a key role in promoting both vasculogenesis and angiogenesis. VEGF plays an important regulatory function in the formation of new blood vessels during embryonic vasculogenesis and in angiogenesis during adult life.
The activities of VEGF are mediated primarily by its interaction with two high-affinity receptor tyrosine kinases: fms-like tyrosine kinase-1 (Flt-1/VEGFR-1) and kinase-insert domain region (KDR/Flk-1/VEGFR-2) both of which are expressed on vascular endothelial cell surfaces. Alternative splicing of Flt-1 results in the production of an endogenously secreted protein referred to as soluble Flt1 (sFlt1), which lacks the cytoplasmic and transmembrane domains but retains the ligand-binding domain [He et al., Mol. Endocrinol. (1999) 13: 537-545]. Thus, sFlt1 can antagonize circulating VEGF by binding it and preventing the interaction of VEGF with its endogenous receptors. sFlt1 also binds and antagonizes placental growth factor (PlGF), another member of the VEGF family, which is produced predominantly in the placenta, as well as of another VEGF family member known as VEGF-B.
VEGF is an important mediator of angiogenesis in a number of pathological conditions including tumor formation and metastasis of solid tumors. Numerous inhibitors of the VEGF/VEGF receptor pathway (e.g. monoclonal antibodies specific for VEGF) have been shown to prevent tumor growth via an antiangiogenic mechanism [Kim et al., Nature (1993) 362(6423):841-4].
Preeclampsia, the most common, dangerous, unpredictable complication of pregnancy is a major cause of maternal, fetal, and neonatal mortality worldwide. While the cause of preeclampsia remains unclear, the principle cause appears to be inadequate blood supply to the placenta making it release hormones or chemical agents that cause maternal endothelial dysfunction, alterations in metabolism and inflammation [Drife J O, Magowan (eds) Clinical Obstetrics and Gynecology, chapter 39, pp 367-370]. These consequently lead to hypertension association with proteinuria in the mother along with impaired placental blood flow, fetal growth restriction and consequential fetal oxidative stress.
During pregnancy, the major source of circulating sFlt1 is the placenta and only minor amounts are produced by other tissues (e.g. by endothelial cells and monocytes). Recent investigations have supported the finding that placental expression and serum levels of sFlt-1 are upregulated in preeclamptic pregnancies, in conjunction with decreased levels of circulating free VEGF and free PlGF, compared to normal pregnancies [Maynard et al., J. Clin. Invest. (2003) 111: 649-658]. The increase in sFlt1, followed by a decrease in free PlGF and free VEGF, was found to precede the onset of clinical disease by several weeks and appears to be more pronounced in severe and early onset preeclampsia [Levine et al., N. Engl. J. Med. (2004) 350: 672-683]. Postpartum, sFlt-1 levels decrease dramatically in both normal and preeclamptic pregnancies [Maynard et al., supra]. Thus, excess sFlt1, by neutralizing VEGF and PlGF, may play a crucial role in the pathogenesis of the maternal syndrome in preeclampsia.
Lam et al. [Lam et al, Hypertension (2005) 46(5): 1077-85] review the possibility of measuring circulating angiogenic proteins (e.g. PlGF) or anti-angiogenic proteins (e.g. sFlt-1) in the blood and urine of pregnant women as a diagnostic and screening tool for predicting preeclampsia. They have examined odds ratios, sensitivity and specificity for various sFlt-1 cutoff values in different trimesters. Lam et al. describe a strong correlation between high sFlt-1 levels and the risk and presence of preeclampsia. Furthermore, they have yielded the conclusion that the higher the sFlt-1 level, the more predictive it is of preeclampsia.
PCT Publication No. WO 2006/069373 discloses methods, compositions and kits for diagnosis of preeclampsia and hypertensive disorders in pregnancy. More specifically, WO 2006/069373 teaches assessment of preeclampsia or predisposition to preeclampsia by monitoring the levels of angiogenic factors, specifically VEGF, PlGF and sFlt-1, in urinary samples of pregnant women. WO 2006/069373 teaches that the higher the level of sFlt-1, the more predictive it is of preeclampsia. Furthermore, according to WO 2006/069373, preeclampsia is associated with a significant decrease in PlGF and significant increase in VEGF urine concentrations.
U.S. Publication No. 20050148040 discloses methods and compositions for screening of gestational disorders (e.g., gestational diabetes, preeclampsia and gestational hypertension) using specific biomarkers. The biomarkers taught are insulin resistance biomarkers [e.g., sex hormone binding globulin (SHBG)] and angiogenesis biomarkers including sFlt-1. More specifically, alterations in two pathways, insulin resistance (e.g., as evidenced by low serum levels of SHBG) and angiogenesis (e.g., as evidenced by low PlGF or high sFlt1), when combined can be used to predict gestational disorders.
U.S. Publication No. 20050025762 discloses methods for diagnosing and treating preeclampsia and eclampsia. U.S. Publication No. 20050025762 teaches treating or preventing preeclampsia and eclampsia using compounds that increase VEGF or PlGF levels (e.g., nicotine, adenosine), using compounds that decrease sFlt-1 levels (e.g., purified sFlt-1 antibody, an sFlt-1 antigen-binding fragment, small interfering RNAs, or double-stranded RNA) such as compounds that bind sFlt-1 and block growth factor binding (e.g., chemical compound, polypeptide, peptide, antibody).